In mobile communications, high user capacities and high data rates are desirable. To achieve this, mobile radio systems have to be highly spectral efficient. Using multicarrier modulation according to OFDM (orthogonal frequency division multiplexing) robust performance and high spectral efficiency can be achieved.
Before the OFDM modulation, a pre-transform can be carried out, resulting in a so-called PT-OFDM (pre-transform OFDM) system.
In [1] (and also in [2]), an iterative detection algorithm for a PT-OFDM system is described. This will be described in the following.
An iteration (corresponding to an iteration index i) of the iterative detection algorithm corresponds to three stages, a reconstruction step, a linear filtering step and a decision step.
In the ith reconstruction step, i.e. in the reconstruction step of the iteration corresponding to the iteration index i, the mith component of the received signal r (received signal vector) is estimated. This is done by using the previously detected symbol {circumflex over (x)}i−1 (i.e. the signal vector detected in the previous iteration). mi corresponds to the frequency domain channel with the ith smallest amplitude. In the filtering step, the cross interference of the data is removed by a linear filter denoted by G. In the detection step, a tentative (hard or soft) decision (denoted by dec(.)) is made to generate the symbol detected in the ith iteration, {circumflex over (x)}i.
The algorithm is initialized with r0=r, {tilde over (x)}=Gr0 and {circumflex over (x)}0=dec({tilde over (x)}0).
The ith iteration is given by:ri=1miri−1+0miΓW{circumflex over (x)}x−1 {tilde over (x)}i=Gri {circumflex over (x)}i=dec({tilde over (x)}i)where 0m is defined as a diagonal matrix with value 1 on its mth diagonal term and 0 otherwise, and 1m as a diagonal matrix with value 0 on its mth diagonal term and 1 otherwise.
In [1], the pre-transform is based on the Walsh-Hadamard transform (WHT) or on other standard transforms.
An object of the invention is to increase the performance of existing transmitting methods.
The object is achieved by the method for transmitting a digital signal, the method for receiving a digital signal, the transmitter and the receiver with the features according to the independent claims.